Method of and apparatus for learning and controlling air-fuel ratio of internal combustion engine

Abstract

A system for learning and controlling the air-fuel ratio of each of divided regions of an operating range of an engine employs a plurality of learning maps in which the engine operating range is divided into regions of different sizes, and these regions are learned in descending order of their sizes. This system improves the convergence of the learning as well as the accuracy of a correction of an air-fuel ratio for each engine operating condition.

I claim: 
     
       1. A method of learning and controlling the air-fuel ratio of an internal combustion engine comprising the steps of dividing the operating range of the internal combustion engine into regions of different sizes; preparing a plurality of learning maps for storing learned air-fuel ratio correction values for the divided regions, respectively, the stored correction values being able to be rewritten; setting a basic fuel supply quantity according to engine operating condition involving at least a parameter related to the quantity of air drawn into the engine; comparing a detected air-fuel ratio of a mixture of gases drawn into the engine with a target air-fuel ratio to set an air-fuel ratio feedback correction value for correcting the basic fuel supply quantity to bring an actual air-fuel ratio close to the target air-fuel ratio; learning a deviation of the air-fuel ratio feedback correction value from a reference value; updating the learned air-fuel ratio correction values of the divided regions of the engine operating range in descending order of the sizes of the devided regions on the learning maps such that the deviation is reduced; and supplying fuel to the engine according to a fuel supply quantity finally set according to the basic fuel supply quantity, the air-fuel ratio feedback correction value, and the learned air-fuel ratio correction value of a corresponding one of the divided regions of the engine operating range. 
     
     
       2. A method of learning and controlling the air-fuel ratio of an internal combustion engine as set forth in claim 1, wherein a deviation of the air-fuel ratio feedback correction value from a target of convergence is detected, and when the deviation exceeds a predetermined extent, the learning process is repeated from the large regions of the engine operating range. 
     
     
       3. A method of learning and controlling the air-fuel ratio of an internal combustion engine as set forth in claim 1, wherein a learned region is found among the divided regions of the engine operating range of the learning map, and according to a learned air-fuel ratio correction value stored for the learned region, learned air-fuel ratio correction values stored for unlearned regions around the learned region are corrected and updated. 
     
     
       4. A method of learning and controlling the air-fuel ratio of an internal combustion engine as set forth in claim 1, wherein a learned air-fuel ratio correction value stored for a particular one of the divided regions of the learning map is rewritten according to learned air-fuel ratio correction values stored in a plurality of subdivided regions contained in the particular divided region. 
     
     
       5. A method of learning and controlling the air-fuel ratio of an internal combustion engine as set forth in claim 1, wherein a learned air-fuel ratio correction value stored for a particular one of the divided regions of the learning map is rewritten after resetting and initializing learned air-fuel ratio correction values stored in a plurality for subdivided regions contained in the particular divided region. 
     
     
       6. An apparatus for learning and controlling the air-fuel ratio of an internal combustion engine comprising: an operating condition detecting means for detecting the operating condition of the engine including at least an operating parameter related to the quantity of air drawn into the engine;   a basic fuel supply quantity setting means for setting a basic fuel supply quantity according to the operating condition detected by the operating condition detecting means;   an air-fuel ratio detecting means for detecting the fir-fuel ratio of a mixture of gases drawn into the engine;   an air-fuel ratio feedback correction value setting means for comparing the air-fuel ratio detected by the air-fuel ratio detecting means with a target air fuel ratio and determining an air-fuel ratio feedback correction value for correcting the basic fuel supply quantity to bring an actual air-fuel ratio close to the target air-fuel ratio;   an learned correction value string means having a plurality of learning maps in which an engine operating range is divided into regions of different sizes, for string learned air-fuel ratio correction values for the respective divided regions of the learning maps, the stored values being able to be rewritten;   a learned correction value rewriting means for learning a deviation of the air-fuel ratio feedback correction value determined by the air-fuel ratio feedback correction value setting means from a target of convergence, and rewriting learned air-fuel ratio correction values stored in the learned correction value storing means one by one to reduce the deviation;   a learning progress control means for controlling the learned correction value rewriting means such that the learned air-fuel ratio correction values stored for the divided regions are rewritten in descending order of the sizes of the divided regions of the learning maps of the learned correction value string means;   a fuel supply quantity setting means for correcting the basic fuel supply quantity according to a learned air-fuel ratio correction value which corresponds to the present engine operating condition and stored in the learning map of the learned correction value string means, as well as the air-fuel ratio feedback correction value, thereby providing a final fuel supply quantity; and   a fuel supply control means for controlling and driving a fuel supply means according to the fuel supply quantity set by the fuel supply quantity setting means.   
     
     
       7. An apparatus for learning and controlling the air-fuel ratio of an internal combustion engine as set forth in claim 6, further comprising a learning repeating means for detecting a deviation of the air-fuel ratio feedback correction value from a target of convergence, and repeating the learning process from the large regions of the engine operating range if the deviation exceeds a predetermined level. 
     
     
       8. An apparatus for learning and controlling the air-fuel ratio of an internal combustion engine as set forth in claim 6, further comprising an unlearned region estimating means for finding a learned region among the divided regions of the learning maps of the learned correction value string means, and according to a learned air-fuel ratio stored in the found learned region, rewriting the air-fuel ratio correction values of unlearned driving regions around the found learned region. 
     
     
       9. An apparatus for learning and controlling the air-fuel ratio of an internal combustion engine as set forth in claim 6, further comprising a means for rewriting the learned correction value of a particular one of the divided regions of the engine operating range of the learning map stored in the learned correction value storing means according to learned air-fuel ratio correction values stored in a plurality of subdivided regions contained in the particular region. 
     
     
       10. An apparatus for learning and controlling the air-fuel ratio of an internal combustion engine s set forth in claim 6, further comprising a resetting means for resetting and initializing the learned air-fuel ratio correction values stored in subdivided regions contained in a particular large region of the engine operating range of the learning map of the learned correction value storing means when learning and rewriting a learned air-fuel ratio correction value of the particular large region.